tube spectral distortion is often different than spectral FET distortion in similar type of circuitries, so tube sound is often different than FET sound. For this reason several sound engineers think that the tube mics are important. However, there are a lot of tubes and a lot of topologies so isn't possible to do an rigorous rule. Infact, I've designed a mic tube with peluso c12, a cinemag trasformer and a triode that sounded more fast and quiet than a lot of (famous) fet mics compared with it, for example. Its sound is however a "tube like sound" yet but isn't the typical vintage tube mic sound that many sound engineer know.
The recording studio that 've bought this tube mic from me says these things I've written about this my mic.
I think that the matter is that several sound engineers think that the tube sound is always those of the vintage tube mics and also, moreover, some electronic engineers think that a mic IC opamp based can sound much better than a tube mic only because they look ad THD value only, but the matter is more complex like seem. A tube circuit distortion can be however less audible than an IC opamp distortion, for example. Or,(as it's very often ) a tube circuit distortion can be more lovely to listen than an IC opamp distortion.
Infact, there are some modern Gefell tube mics, designed as modern items, that however many sound engineers do not change with other SS or vintage tube items.